This invention relates to the field of prosthetics, and more particularly, to an intervertebral disc prosthesis designed to replace a damaged intervertebral disc.
The human spine consists of twenty-four small bones known as vertebrae, or “vertebral bodies,” that protect the spinal cord and provide stability to the torso. The vertebrae are arranged in a column and stacked vertically upon each other. Between each vertebra is a fibrous bundle of tissue called an intervertebral disc. These intervertebral discs act as a cushion to the spinal column by absorbing the shock and pressure associated with everyday movement. They also prevent the vertebrae from rubbing against each other.
Each intervertebral disc comprises two distinct regions. A firm outer region maintains the shape of the intervertebral disc. An inner region provides a soft spongy tissue that enables the disc to function as a shock absorber. Over time, the normal aging process causes the intervertebral discs to degenerate, diminishing their water content and thereby reducing their ability to properly absorb the impact associated with spinal movements. Diminished water content in the intervertebral discs may also cause the vertebrae to move closer together. Tears and scar tissue can weaken the discs, resulting in injury. When the discs wear out or are otherwise injured, they do not function normally and may cause pain and limit activity. Such injury may result in a condition known as degenerative disc disease.
The condition of degenerative disc disease can potentially be relieved by a surgical procedure called artificial disc replacement. In this procedure, the damaged intervertebral disc is replaced by a prosthetic disc. One well known intervertebral prosthetic disc is produced by DePuy Spine, Inc. of Raynaham, Mass. and is sold under the trademark CHARITE®.
Although current intervertebral disc prosthetic devices have enjoyed success, it would be desirable to add additional desirable features to the prosthetic device. For example, for it would be desirable to provide a three-piece prosthetic disc design including a core sandwiched between a superior plate and an inferior plate where the core is secured to the inferior plate using a simple press-fit arrangement and the core is restricted from rotating relative to the inferior plate. Additionally, it would be advantageous to design the intervertebral disc prosthesis wherein the prosthesis may be more easily grasped and retained by an insertion tool in order to facilitate implantation of the prosthesis in the patient.